How did Joe explain his solution for five times nine to Johnny, based on the Math Talk posters?

The correct choice highlights the process of counting by fives, which is a practical way to understand multiplication, particularly with a factor like nine. When Joe explained his solution for five times nine by counting by fives, he was essentially demonstrating that multiplication is a form of repeated addition.

By counting five repeatedly for a total of nine times, Joe is showing how multiplication operates. Specifically, he would say 5, 10, 15, 20, 25, 30, 35, 40, 45, progressively adding five each time up to nine counts, clearly illustrating that (5 \times 9) equals 45. This method aligns well with the concept of multiplication as an additive process and helps in developing a deeper understanding of the operation, rather than simply memorizing multiplication facts.

This makes Joe's explanation effective, as it connects to foundational math concepts that can be visualized and understood through counting.